Skip to main content

Full text of "Some abnormal water relations in citrus trees of the arid Southwest and their possible significance"

See other formats


UNIVERSITY OF CALIFORNIA PUBLICATIONS 
IN 


AGRICULTURAL SCIENCES 
Vol. 3, No. 3,’pp. 37-54, plate 12 September 29, 1917 


SOME ABNORMAL WATER RELATIONS IN 
CITRUS TREES OF THE ARID SOUTH- 
WEST AND THEIR POSSIBLE 
SIGNIFICANCE 


BY 
~ ROBERT W. HODGSON 
" 


UNIVERSITY OF CALIFORNIA PRESS 
BERKELEY 


(2-) ¢ 
Very 
U 7 


~ Monagrag: 


UNIVERSITY OF CALIFORNIA PUBLICATIONS 


Note.—The University of California Publications are offered in exchange for the publi- 
cations of learned societies and institutions, universities and libraries. Complete lists of — 
all the publications of the University will be sent upon request. For sample copies, lists of . 
publications and other information, address the Manager of the University Press, Berkeley, 
Oalifornia, U. 8. A. All matter sent in exchange should be: addressed to The Exchange 
Department, University Library, Berkeley, Caloris, U.S. A. é 


AGRICULTURAL SCIENCES.—Charles B. Lipman, Ernest B. Babcock, and John W. 
Gilmore, Editors: Price per volume, $5. 
Vol. 1. 1. The Distribution. and Activities of Bacterfa in Soils of the Arid 
Region, by Charles B. Lipman. Pp. 1-21. October, 1912 ... ww... .- $0.20. 
%. Studies on the Phenoldisulphonie Acid Method for Determining Nitrates : 
in Soils, by C. B. Lipman and L. T. Sharp. Pp. 23-37. October, 1912. 15 — 
8. The Effects of Calcium and Magnesium Carbonates on Some Biological 
Transformations of Nitrogen in Soils, by W. P. Kelley. Pp. 39-49. - y 
December, 1912... ae ec Peat eet pine eS Tg AS Aa? 4 | 
4, The Aluminum Reduction Meth od as. Applied ‘to the Determination of 
Nitrates in ‘‘Allkali’’ Soils, by Paul S. Burgess. Pp. 61-62. May, 


1913 : 15 
5. Studies Upon Influences Affecting the Protein Content of Wheat, by G. 
W.Shaw<e-Pp.63-126: ; October, 1913-2 ae Se ee “75 
6, The Effect.of Copper, Zinc, Iron and Lead Salts on Ammonification and~ ; 
Nitrification in Soils, by C. B. Lipmar and P, 8. Burgess, Pp. 127- st ee 
PSO rare LST oe a a SS aaeapeee avon fac teenth eso ne eR AGS 
7. Studies on Ammonification in Soils by Pure Cultures, by C. B. Lipman Ex 
and P. S. Burgess. Pp. 141-172. April, 1914 202n.cc ccs ceceteneeen SS uk 


8. Humuts and Humus-Nitrogen in California Soil Columns, by &. H. : 
Loughridge. Pp, 173-274. August, 1914 20... occ. cececccceeesreeenene, O00 ~ 
8. New Experiments on Alkali Soil Treatment (Preliminary. Report), by 2 
Charles B. Lipman and Leslie TI. Sharp. Pp. 275-290,- plates 1-4, ele 
Pi fot (Sear Ce Bs eta tah Ne chap cS eae rahe NaS AE PremS Ali CUE ane et MceAa ee eS “15. 


10. Fundamental Interrelationships between Certain Soluble Salts and Soil _ 
Colloids, by L..T. Sharp. Pp. 291-339. April, 1916 __-.. 2 50 


11. Influence of the Composition and Concentration of the Nutrient Solu- oe ; 


tion on Plants Grown in Sand Cultures, by Arthur Hugo Ayres, Pp. 


$41:594, pls, B-15.- January, AGL, oy.c 2c. aie hue eee “60 
12. Certain Effects under Irrigation of Copper Compounds upon Crops, by ze 
R. H. Forbes. Pp. 395-494, plates 6-9. April, 1917 %222 2. 1,00 


18. Experiments on the Effects of Constituents of Solid Smelter Wastes on 
Barley Growth in Pot Cultures, by C. B. Lipman and W, F. Gericke. 


Bp, 495-587. March; 1917. ot ks eh ee a 


Vol. 2. 1, Studies in Juglans I. Study of-a New Form of Juglans Californica 

Watson, by Ernest B. Babcock. Pp. 1-46, plates 1-12. December, 

1913 

2. Studies in Juglans. ‘Ti. Further Observations on a New ¥V 
Juglans Californica Watson and on Certain Supposed Walnut-Oak 

Hybrids, by Ernest B. Babcock. Pp. 47-70, Plates 13-19. October, ‘a 

SN nr a ae ea wpmsge act Sta lace cen Siecle oS can eee pes SE oe ae er gag 35) 


8. Studies in Juglans, TII: (1) Further Evidence that the Oak-like Walnut 
Originates by Mutation, by Ermmest. B. Babcock. Pp. ese: pls. 20-21. 
Séptentbior, TOG Se a ee arenes -10 
Vol. 8. 1. New Grasses for California, I, Phalaris stenoptera Hack,, by” P. B. Ken- : 
nedy. Pp. 1-24; plates-1-8.° Tully) 19VT. 5-2 oe aoa ance petetcsee cece ean dabanarane “30 


i) 


. Optimum Moisture Conditions for Young Lemon Trees on a Loam Soil, 
by L. W. Fowler and C. B. Lipman, Pp. 25-36, plates 9-11. Sep- 
PeImbere LOL. sa ee Se ae a hk as ged aera eeetek aan ne pth There 

Some Abnormal Water Relations in Citrus Trees of the Arid South- vg 
west and their Possible Significance, by Robert W. Hodgson. Pp. 
87-54, plate 12... September, 1907 ovo scc eee ease se isso casccetponed ons ete ery] ae 


& 


AGRICULTURE,—The Publications of the Agricultural Experiment Station consist of Bul- 
letins and Biennial Reports, edited by~Professor Thomas Forsyth Hunt, 
Director of the Station. These are sent gratis to citizens of the State of 
California. For detailed information regarding them address The Agri- 
cultural Experiment Station, Berkeley, California, ; 3 
1), of DD. 


5 AF 


UNIVERSITY OF CALIFORNIA PUBLICATIONS 


AGRICULTURAL SCIENCES 


Vol. 3, No. 3, pp. 37-54, plate 12 September 29, 1917 


SOME ABNORMAL WATER RELATIONS IN 
CITRUS TREES OF THE ARID SOUTH- 
WEST AND THEIR POSSIBLE 
SIGNIFICANCE 


BY 
ROBERT W. HODGSON 


INTRODUCTION 


The progress of the development of the citrus industry, in general, 
and that of California in particular, has frequently been retarded or 
temporarily stopped by serious obstacles in the form of insect pests 
or plant diseases. Some of the most baffling of these troubles fall 
naturally into a group which for want of a better name has come to 
be known as that of ‘‘ physiological diseases,’’ which are thought to be 
caused by various obscure derangements of nutrition or other vital 
functions. This group includes mottled-leaf, die-back, chlorosis, June 
drop, puffing of the fruit, and others of less importance. Knowledge 
of the true nature of this class of diseases is extremely meager in spite 
of the fact that they have received much earnest attention from scien- 
tific investigators; and little can be accomplished in the way of devis- 
ing control measures until much more is known in regard to them. 
Nor can we hope to progress far beyond the realm of speculation with- 
out greatly augmenting our knowledge of the physiology and anatomy 
of the normal citrus tree when grown under any one of a series of 
very widely varying environmental complexes which obtain in differ- 
ent parts of the arid southwest. 

It is, therefore, proposed to attempt by means of a series of sys- 
tematic experimental studies to obtain some definite and accurate 
information on the physiology of the genus Citrus. It is hoped that 
the results may serve as a basis for the elucidation of some, at least, 


3 University of California Publications in Agricultural Sciences  [Vol.3 


of the important problems referred to above. The studies in ques- 
tion will attempt to shed light on transpiration problems, nutrition 
problems, and others equally important. The paper which is sub- 
mitted herewith forms an introductory contribution to the subject 
under investigation. 

The writer is not unaware of the essential similarity between the 
physiological problems presented by citrus and other fruit trees. He 
has chosen, however, to study the physiology of the citrus tree as a 
separate entity because of the reasons given above, and the further 
one that the peculiar climatie conditions under which this tree is 
frequently placed in the arid southwest, demand a special treatment. 
Doubtless much may be gained from these studies which will apply 
to physiological problems connected with other trees, 

The data here presented were obtained during an investigation of 
one of the so-called physiological diseases above mentioned, namely, 
the June drop.t Ever since the Washington Navel orange has been 
grown in the dry interior valleys of Arizona and California, this 
variety has been subject to excessive dropping of the young fruits. 
This has came to be known popularly as the June drop although the 
fall of the fruits is by no means confined to June but may oceur at 
any time from petal fall, in April, until the fruit reaches several 
inches in diameter in August. The prevalence and amount of this 
dropping seems to be influenced to a marked degree by certain 
environmental factors to which the trees are subject. The regular 
annual shedding of the young fruits is most serious in regions where 
the annual precipitation is lowest, the mean summer temperature 
highest, atmospheric humidity lowest, solar radiation most intense, 
and air movement greatest during the growing season. That the 
excessive drop of young fruit is in some way intimately connected 
with extreme climatic conditions is indicated by the fact that in some 
parts of southern California, where the drop is ordinarily not excess- 
ive, the hot wave of June 15-17, 1917, durimg which a temperature 
of 118° F was experienced in the Riverside and Redlands districts, 
was immediately followed by a drop so severe that practically the 
entire young crop of navel oranges was lost. 

The experimental work from which the data were obtained was 
carried on at Edison, Kern County, California. Edison comprises 
"1 This investigation, which is now in progress, was carried on in collabora- 
tion with Professor J. Eliot Coit who planned the first series of experiments 
and began the work in February, 1916. A joint-authorship paper correlating 


this and other aspects of the June drop phenomenon is in course of prepara- 
tion. 


1917] Hodgson: Abnormal Water Relations in Citrus Trees 39 


a small colony of about seven hundred aeres of orange orchard 
located eight miles southeast of Bakersfield and surrounded on two 
sides by typical desert of the southern San Joaquin valley, with its 
characteristic semixerophytiec flora. Extreme climatie conditions, as 
above mentioned, are operative there but the Washington Navel 
orange matures early and is of excellent quality, although crops are 
small because the drop referred to is excessive. 


Water RELATIONS AND ABSCISSION 


It has long been recognized that abnormalities or irregularities in 
the water relations of plants are often associated with the abscission 
of various plant parts. Balls? was able to cause complete shedding 
of leaves, flower buds, and bolls of the cotton plant Gossypium her- 
bacewm within four days by pruning the roots and so limiting the 
ability of the plant to take up water. Lloyd* in his investigation of 
the cause of abscission in the same plant came to the conclusion that 
the causative factor lay in a steady decrease in the moisture content 
of the soil in contact with the roots of the plant. This reduction 
causes a severe tax on the power of the plant to maintain normal 
water relations and results in fluctuations in the water content of 
the aerial parts which, in turn, leads to abscission. 

Although the work of Lloyd was performed in the humid southern 
states, he makes the statement that ‘‘there seldom oceurs a day on 
which there is no minus water fluctuation in the plant.’’ He based 
this conclusion not only on data derived from shedding reeords but 
also on a study of transpiration rates, and water deficit in the leaves. 
In connection with his observations on the effect of temperature in 
causing acceleration of abscission, he came to the conclusion that ‘‘the 
water deficit is the cause of the rise of temperature in the tissues and 
that this constitutes the stimulus which directly leads to abscission.’’ 

Other evidence of the occurrence of marked deficits in the water 
content of plant organs is not lacking. Livingston and Brown,* work- 
ing with a number of plants growing near Tuscon, Arizona, found 
that (with the exception of the true xerophytes as Covillea and 
Prosopis) during the afternoon the leaves suffered a marked decrease 
in water content which was made up during the night. This periodic 

2 Cairo Sci. Jour., vol. 5, p. 221, 1911. 

3 Trans. Royal Soc. Can., ser. 3, vol. 10, p. 55, 1916, see also Bull. Torr. Bot. 


Club, vol. 40, p. 1-26, Jan., 1913. 
4 Bot. Gaz, vol. 53, p. 319, April, 1912. 


40 University of California Publications in Agricultural Sciences  [Vol.3 


diurnal condition of dessication has been found by Livingston and 
Brown to serve as a check on the absolute transpiration and has been 
termed ‘‘incipient drying.’’ Lloyd’ independently obtained similar 
results in his investigations on Fouquieria splendens and Mrs. Shreve® 
established the same phenomonon in 1913 with Parkinsonia micro- 
phylla. 

Inasmuch as the genus Citrus is undoubtedly a mesophyte of 
tropical origin and therefore grown in the interior valleys of Cali- 
fornia under purely artificial conditions,’ it would naturally be 
expected that the abnormal water relations above discussed might 
obtain to an unusual degree, especially during the hot growing period, 
when the ability of the plant to make up for excessive transpiration 
is taxed to the limit. Citrus fruits are borne on wood of the current 
season’s growth which ordinarily bears six to eight leaves on the same 
fruiting shoot. Therefore, it seemed reasonable that under conditions 
of excessive transpiration the leaves might draw on the water supply 
of the fruits and thus bring about an abnormal water relation. With 
the above considerations in mind it occurred to the writer that this 
premature fall of the fruits might be due to irregularities or abnormal- 
ities in the water relations between the fruits and foliage, resulting in 
abscission in some way analagous to the shedding of cotton bolls under 
the stimulus of a water deficit. 

The method used in obtaining the data here presented consisted 
in the main of simple moisture determinations of leaves and fruits of 
various kinds taken at different hours of the day. The material was 
gathered and quickly placed in weighing cups fitted with ground 
glass covers. After weighing, the material was thoroughly dried 
and then reweighed. For convenience in the case of fruits and large 
leaves, the material was cut into small pieces. The calculations are 
based on the dry weight of the material, except as otherwise stated. 
The data obtained are shown in condensed form in table 1. The 
figures shown represent averages of at least ten duplicate determina- 
tions, and in most instances of more. 

The data presented in table 1 show some very interesting condi- 
tions. It is quite clear that, with the exception of the new succulent 
growth, the young fruits are at all times higher in water content than 
the leaves situated near them. These data also seem to leave no doubt 


5 Plant World, vol. 15, p. 11, 1912. 
6 Ann. Rpt. Dir. Bot. Res. C. I. W., Feb. 12, 1913, p. 81. 


7 For a more complete discussion see Livingston, B. E., ‘‘A single index to 
represent both moisture and temperature conditions as related to plants.’’ 
Physiological Researches, vol. I, No. 9, April, 1916. 


1917] Hodgson: Abnormal Water Relations in Citrus Trees 41 


TABLE 1 


AVERAGE MOISTURE CONTENT 
Average water content 


in per cent 
Kind of material (Dry weight) 
New leaves about two weeks old 242.0 
Full grown leaves of current season’s growth 162.2 


Leaves of one season’s growth—about one year old ............ 132.7 


Leaves of two season’s growth—about two years old _ 126.1 
Leaves of three or more season ’s growth. Over two years 

OL Cae eens aati ase nec ecs ost cecrpeencesaracsenensaee=s 117.6 
Leaves of current season’s growth. Gathered between 

OURAC Maw 20 pile pea Mien eee meee me ere ons c seco Luster scencasaeucececseresaseas 164.9 
Same gathered between 1 P.M. and 4 P.M 157.2 
Leaves of current season’s growth gathered from eelinindl 

LUULES MD Ete CW OM Aci ANG G2) Mie) cee nccereceneececeemnstennsnacncnasnasureac= 166.8 
Same gathered between 1 P.M. and 4 P.M. —.........-.-.------eeeee- 160.4 
Fruits destined to subsequent abscission, one-third to three- 

PF OMI HAS me @ aT OMAN GOT ceressaseccactencsaxwecccc ne secenncecacnaxewse-rerenees 191.5 
Fruits apparently normal gathered between 9 A.M. and 12 M.8 260.2 
Same gathered between 1 P.M. and 4 P.M. .....--.----.---------c-eeceo-- 247.7 
Fruits destined to subsequent abscission gathered between 

OB) DRAIN, mL IN epee ener aoe see Sor See EEE SE ES SE EEE 201.4 
Same gathered between 1 P.M. and 4 P.M. ~.......--...----.--cseeeeeee+ 179.2 


of the fact that as the leaves grow older there is a progressive decrease 
in water content. 

It is also quite evident that a regular diurnal decrease in the water 
content of leaves of the current season’s growth is manifest during 
the afternoon. Such leaves averaged 164.9% in water content for the 
period between 9 a.m. and 12 m. and only 157.2% for the period 
between 1 p.m. and 4 p.m. This difference does not appear significant 
when viewed in the light of the large differences obtained by Living- 
ston and Brown with some of their material. However, it should 
be borne in mind that those authors were dealing, for the most part, 
with much more succulent plants containing a large amount of water 
storage tissue. Further, it should be noted that these figures are 
averages, since the determinations on which they are based were not 
made at the same hours. Individual pairs of determinations fre- 
quently showed differences of as much as 25% to 30% in as short a 
period as six hours. On June 5 at 2:30 p.m., with the temperature at 
95° F and the relative humidity at 19%, the water content of leaves 
of the current season’s growth was 144.3%. At 4 a.m. the next morn- 
8 The fruits used for these determinations averaged a little larger than 


those gathered in the forenoon and therefore would normally be somewhat 
higher in water content. 


42 University of California Publications in Agricultural Sciences [Vol. 3 


ing, with the temperature at 62° F. and the humidity 54%, the water 
content of similar leaves was found to be 172.6%, showing a differ- 
ence of 28.3%. This phenomenon is taken to indicate the presence of 
incipient drying in citrus and is in full accord with the results of 
the writers above mentioned as well as with those obtained by Lloyd. 

Since the young fruits have a higher water content than adjoin- 
ing leaves which, in turn, exhibit a diurnal decrease in relative water 
content, the conclusion, a priori, that the leaves might possibly draw 
on the water supply of the fruit during periods of excessive transpira- 
tion seemed entirely plausible. If such is the case it would seem that 
leaves so favorably situated should not show this daily variation, at 
least to the degree shown in the leaves not so favorably situated. The 
data in table 1 show, however, that the average difference in water 
content of the two sorts of leaves gathered in the forenoon and after- 
noon is quite small. This is taken to indicate that if such leaves do 
utilize the water supply of the fruits, the evaporating power of the 
atmosphere is so strong that as fast as they receive this surplus water, 
it is lost and thus causes no appreciable difference in their relative 
water content. 

The next step was to ascertain the water content of different kinds 
of fruits, those destined to remain and mature, and those showing 
indications of subsequent abscission. It is quite easy to distinguish 
between the two, from a week to ten days before abscission occurs, 
by the difference in their appearance. Exposed fruits destined to 
drop exhibit a small yellow spot about the navel end several weeks 
before the actual drop occurs. This spot gradually extends and 
spreads until at abscission it usually occupies at least half the area 
of the fruit. In the ease of well-shaded fruits, the yellow color is 
evenly distributed over the entire surface. A large number of mois- 
ture determinations were made which showed that those fruits destined 
to subsequent abscission averaged 59% less water than those fruits 
destined to remain and mature. (See table 1.) The presence of this 
condition in the fruits, especially when considered in connection with 
the daily inerease at certain hours in the water deficit of the leaves 
immediately behind them, seems to point to the possibility of the leaves 
depriving the fruit of a part of their normal water supply. It cer- 
tainly indicates an abnormal water relation. 

Lemon growers prune their trees at all seasons of the year, even 
while the fruit is still on the trees. It is a well established practice to 
gather the good fruit from the excised branches immediately, in order 
to prevent it from becoming flaccid. Inasmuch as the fruit, as ordi- 


1917] Hodgson: Abnormal Water Relations in Citrus Trees 43 


narily picked from the tree, remains turgid for several months, it is 
the common belief that the leaves draw the water out of the fruit when 
the branch is severed from the tree. That this is exactly what does 
occur, when the leaves are deprived of their normal water supply, is 
shown by the following experiments: 

Experiment 1— Two shoots bearing small terminal oranges of 
approximately the same size and having the same number of leaves 
and approximately the same leaf area, were taken to the laboratory, 
placed on the table and allowed to dry under similar conditions except 
that in one case the fruit was severed from the stem. All cut surfaces 
were sealed with vaseline. 

Within twelve hours a marked difference in appearance was 
observed. The leaves on the shoot from which the orange was detached 
were considerably shriveled while those on the other shoot remained 
turgid and fresh. This difference became more pronounced as time 
elapsed and in thirty hours a distinct difference in the appearance of 
the fruits as well as leaves was visible. The detached fruit remained 
firm and retained its dark green color and lustre while the attached 
fruit was soft and flaccid and exhibited a dull green color without 
lustre. This experiment was performed repeatedly with both oranges 
and lemons with the same results. (See plate 12, fig. 1.) 

As all the eut surfaces were sealed, it seems clear that the leaves 
on the shoot with fruit attached actually drew on its water content 
and that it was this supply of water which enabled them to remain 
alive and fresh long after the leaves on the other shoot had withered 
and died. 

Heperiment 2—Quantitative data on water content were desired 
to substantiate the visible indications described in Experiment 1. 
Therefore the latter was repeated several times and moisture determin- 
ations on leaves and fruits were made at various periods. <A repre- 
sentative set of such determinations is given in table 2: 


TABLE 2 


MOoIstuRE CONTENT DETERMINATIONS, TWENTY-FOUR Hours AFTER BEGINNING 
OF EXPERIMENT 2 


Weight of Weight of Weight of Water con- 
container and same when material in tent per 
Kind of material fresh material dry grams cent 
in grams 
Orange detached from branch...... 23.40 21.670 2.665 185.0 
Orange attached to branch... 23.585 22.367 2.075 142.1 


Leaves from branch {21.831 21.805 aul eee 
with fruit removed ] 22.045 22.010 170 21.4 avg. 
Leaves from branch {21.845 21.275 SLO peers 


with fruit attached ) 20.604 20.477 .284 73.7 avg. 


44 University of California Publications in Agricultural Sciences  [.Vol.3 


These data show that after twenty-four hours the leaves on the 
shoot with orange attached contained an average of 52.3% more water 
than those on the other shoot. They further show that the detached 
fruit contained 42.9% more water than the attached fruit from which 
the leaves had been drawing their supply. This is considered to be 
conclusive evidence that in the case of excised branches the leaves 
can draw water from the fruit. 

Experiment 3—Two shoots in every respect similar to those used 
in the previous experiments were treated in the same manner as those 
of Experiment 1 and 2. These were then weighed at irregular inter- 
vals until they had reached a constant weight. During the interim 
they were kept on the laboratory table. The data obtained are found 
summarized in table 3: 

TABLE 3 


WATER CONTENT DETERMINATIONS MaAprE AT IRREGULAR INTERVALS BASED ON 
THE WHOLE WEIGHT 


Shoot with orange attached Shoot with orange detached 

Number Weight Loss in Lossin Difference Gyeigit ~ Geasia’| Ghossan Dinerenee 

of hours in grams grams per cent in in grams in grams__ per cent in 

elapsed per cent per cent 

0 AS TI2i ii) accra recs sees ATT. ey ae ee 
3 4.436 438 8.9 6 4.380 397 8.3 aes 

19 3.957 -915 18.7 ae 3.830 947 19.8 iat 
21 3.895 977 20.0 ie 3.742 1.035 21.7 ila? 
24 8.803 1.069 21.9 s 3.607 1.170 24.4 2.5 
26 3.683 1.189 24.4 = 3.442 1.835 27.9 3.5 
27 3.610 1.262 25.9 aa 3.342 1.435 30.0 4.1 
44 3.263 1.609 33.0 meee 2.911 1.866 39.1 6.0 
49 3.047 1.825 37.4 Ses 2.682 2.095 34.8 6.4 
51 2.920 1.952 40.0 Aon 2.575 2.202 36.0 6.0 
91 2.125 2.747 56.3 eee 2.008 2.769 57.9 1.6 
96 2.053 2.819 57.8 = 1.960 2.817 58.9 ail 
99 2.000 2.872 58.9 ae 1.9385 2.842 59.5 6 

116 1.921 2.951 60.5 vce 1.873 2.904 60.8 3) 

119 1.894 2.978 Gel a 1.852 2.925 61.2 alll 

121 1.881 2.991 61.3 ease 1.844 2.933 61.4 1 

140 1.825 3.041 62.5 4 1.807 2.970 62.1 

146 OM 3.075 63.1 o 1.783 2.994 62.6 

162 1.774 3.098 63.5 6 1.770 3.007 62.9 

186 1.736 3.136 64.3 8 1.743 3.084 63.5 

195 1.717 3.155 64.7 9 1.726 3.051 63.8 

211 1.705 3.167 65.0 1.1 1.720 3.057 63.9 

218 1.695 3.177 65.2 1.0 1.710 3.067 64.2 

260 1.666 3.206 65.8 Alea 1.686 3.091 64.7 

285 1.652 3.220 66.0 a ll 1.675 3.102 64.9 

306 1.642 3.230 66.2 atl 1.664 3.113 65.1 

330 1.631 3.241 66.5 alsa 1.652 3.125 65.4 


525 1.613 3.259 66.8 1.0 1.631 3.146 65.8 


1917] Hodgson: Abnormal Water Relations in Citrus Trees 45 


The data in this table indicate that the amount of water in the 
fruit available for use by the leaves was sufficient to maintain the 
latter alive for approximately 50 hours after the shoot was cut from 
the tree. It is further evident that when three hours had passed the 
leaves on the shoot with fruit attached had not yet begun to take water 
from the fruit to any appreciable extent because the shoot with fruit 
detached shows less water loss than the shoot with fruit attached. 
However, this condition was soon reversed and the leaves began to 


20 40 60 80 100 120 140 160 180 200 220 


Fig. 1. Showing the difference in per cent of water loss of shoot with 
orange attached and shoot with orange detached. The water loss curve of the 
shoot with fruit detached is considered as normal. .Ordinates represent differ- 
ences in per cent of water loss, abscissae, the time elapsed in hours. Water 
content calculated on basis of fresh weight. 


draw on the water in the fruit while the leaves to which no water was 
available from the fruit showed indications of wilting. 

That shortly after 50 hours had passed death oecurred in the 
leaves of the shoot with fruit attached is shown by the rapid increase 
in the amount of water loss. This was undoubtedly due to increased 
permeability of the cytoplasmic cell membranes after death. After 
50 hours the difference in water content of the two was 18.3% in 
favor of the shoot with fruit attached. However, from this time on 
until both had reached a constant rate of water loss (after about 200 


46 University of California Publications in Agricultural Sciences  [Vol.3 
hours), this shoot lost water more rapidly than the shoot with fruit 
detached. These relations are very clearly shown in figure 1. The 
normal water loss curve is illustrated in figure 2. 

Experiment 4—A forked twig bearing a small terminal fruit on 
each branch was selected and cut. The fruits were immediately im- 
mersed in water and the shoot tied to a support in such a fashion 
that all the leaves were exposed to the air, the fruits alone being 
immersed. One orange was now removed by cutting it under water 
and all cut surfaces were sealed. The two fruits remained under 


64 
56 
48 


40 


16 


50 100 150 200 250 300 350 400 450 500 


Fig. 2. Showing the general type of water loss curve of a shoot detached 
from the tree, including detached orange. Ordinates represent water loss in 
per cent and abscissae, the time elapsed in hours. 


water. The container and support were then placed on a bench in 
the shade in the open air and left for fifteen hours, at the end of 
which time moisture determinations were made on the fruits. 


TABLE 4 
MoIstuRE DETERMINATIONS AFTER FIFTEEN Hours 
Weight of Weight of Weight of Water con- 
container and same when material in tent per 
Kind of material fresh material dry in grams cent 

in grams grams 
Detached orange ..... seccseeeeeces- 24,680 21.435 3.330 206.9 
Attached orange: 2-222 -2n. 23.210 21.773 2.570 126.8 


1917] Hodgson: Abnormal Water Relations in Citrus Trees 47 


The data in table 4 show that at the end of fifteen hours there was 
a difference in water content between the two fruits of 80.1%. There 
seems to be no way of accounting for this large difference other than 
that the leaves had actually drawn the major part of it at least, from 
the attached fruit. 


Water TRANSPORT Stupres BY Means or Dyk SturF SoLutions 

Experiment 5—Bearing the foregoing findings in mind, it seemed 
desirable to determine something of the nature of this reversal of 
normal water flow by means of dye solutions. Accordingly a shoot 
bearing a terminal fruit was cut from the tree and the orange pared 
away at the apical end to open the tracheal elements and admit the 
dye.’ This paring was done under the solution to prevent the entrance 
of air bubbles. Water soluble eosin was used. The orange was 
immersed in the liquid for a half hour, after which the shoot was 
split open. The tracheal tubes throughout all parts of the leaves, 
stems and fruits were found to be strongly stained. 

Experiment 6—It seemed desirable to simulate the actual situation 
on the tree as nearly as possible and the following experiment was 
designed to accomplish this. A crooked fruiting branch bearing a 
number of small lateral shoots and leaves, and one terminal orange 
was cut under water. The eut end was kept under water and the 
branch so supported that the fruit was immersed in an eosin solution. 
The apex of the orange was then pared as described above. The 
branch then rested with its basal end in water and the vascular 
bundles of the fruit open to eosin at the other end of the branch. 
(See pl. 12, fig. 2.) If we substitute for the water container the con- 
ducting system of the tree, and for the watery solution of eosin the 
developing fruit high in water content, we have very similar conditions 
to those existing in the experiment, save for the fact that the fruit is 
not open to the air and the conducting system bears a certain relation 
to the rest of the tree. 

The experiment was begun late in the afternoon and the branch 
left outdoors over night. At 8 o’clock the next morning the leaves 
were examined and found to be very fresh and turgid. Indeed they 
were noticeably much fresher in appearance than they had been the 
evening before. On careful examination absolutely no trace of eosin 

9Tt should be stated here that the Washington Navel orange is in reality 
a double fruit, with a small secondary orange within a large primary fruit. 
This interior fruit constitutes what is known as the navel and it possesses an 
independent vascular system of its own which traverses the central pith of 


the primary fruit before ramifying through the secondary orange. This central 
pith thus acts as the stem to the small fruit. 


50 University of California Publications in Agricultural Sciences [Vol.3 


ing between 50-100 per square millimeter as compared to 300-450 per 
square millimeter on the leaves. Measurements of the leaves situated 
within six inches of the fruit showed that, in addition the leaf area 
immediately behind the young growing fruit is larger than the area of 
the fruit until it reaches approximately two inches in diameter, after 
which falling of the fruit is comparatively rare. Therefore, it seems 
highly probable that the transpiration of the fruit as compared to 
that of the leaves situated immediately behind it is an almost negligible 
factor and it appears reasonably certain that either water is actually 
drawn back or that the normal supply is decreased. 

Considering these two possibilities, the first merits more considera- 
tion as it is supported by proof which, though not absolute, is at least 
presumptive evidence of a strong enough character ; while on the other 
hand the second possibility, agreeing though it does with the most 
recent theory on sap movements in plants as put forth by Dixon, is 
still a theoretical consideration. According to this theory, which pos- 
tulates strong tensions existing in the ascending water columns, no 
assumption of an actual reversal of the current is necessary in order 
to explain a decrease in moisture content. During normal conditions 
the relation between the tensions existing in the water columns leading 
to the fruits and those leading to the leaves is such that both organs 
receive an adequate water supply. The tension existing in any one 
of these water columns is a function of the transpiring force existing 
in the transpiring plant organ as modified by atmospheric conditions. 
Therefore, as these transpiring forees vary, the tensions vary. Trans- 
piration from the leaves, for reasons pointed out above, is subject to 
much greater variation than that from the fruits. Therefore during 
periods when evaporation is greatly accelerated the tensions in those 
water columns leading to the leaves are greatly increased and as a 
consequence more water is drawn to them. As the source of supply 
in the conducting system is practically constant, the amount in the 
fruits is thereby reduced and this results in a decrease of relative 
water content of a magnitude conditioned by the transpiration of the 
fruit. 

However, it should be noted that the data in table 1 show a 
decrease in absolute water content of the fruit of 15% to 20%, a loss 
of considerable magnitude. There are only two ways in which such 
a decrease in absolute water content can take place: (1) the water 
is lost by transpiration from the fruit, or (2) it is drawn back by 
the leaves. But since the fruit possesses a very small stomatal area 


1917] Hodgson: Abnormal Water Relations in Citrus Trees 51 


as compared with the leaves and, moreover, it is highly probable that 
a large percentage of this area is non-functional, being obstructed 
by accumulations of a resinous nature, there is small likelihood for 
absolute loss of water in this manner to the extent noted. Hence 
there seems but one way to explain it and that is by movement back 
from the fruits. 

Evidence of an indirect nature pointing to the same conclusion 
lies in the fact that there are some indications that abscission of a 
certain proportion of the young fruits is directly due to the influence 
of hydrolysing enzymes secreted by certain saprophytie or facultative 
parasitic fungi always found present on the shriveled style and fre- 
quently in the proliferations of the navel. Such enzymes in order to 
act on the abscission layer must be drawn back through the vascular 
systems of the fruit imto the pedicel where this layer is located. 
Investigations on this point are now in progress. 

Experiment 7—Three similar fruits were selected on different 
parts of a tree; on one of the lower branches in the shade, at a height 
of four feet, and in the top of the tree in full sunlight. At noon each 
fruit was pared so as to admit entrance of a solution and then plunged 
quickly into a small vial containing a watery solution of eosin. These 
vials were securely tied to the shoot and left suspended for two hours. 
At the end of that time, on cutting leaves from these shoots, eosin 
staining was found in the vascular systems of all. On examining back- 
ward toward the tree, eosin was found as far back as thirty centi- 
meters. This experiment was repeated a number of times both at 
Edison and at Riverside and uniformly gave the same results, although 
much less marked at the latter place. In every ease the backward 
movement of the eosin solution was at its maximum during the 
afternoon. 

Cutting the ends of branches in situ under a watery solution of 
eosin was tried at different times of day and gave similar results. 
This experiment was performed at Edison, Riverside and Indio. At 
the latter place, with the temperature at 116° F and the humidity at 
8% the eosin solution traveled backward at the astonishing rate of 
30cm. per minute at 6 p.m. Similar results were obtained using 
Eucalyptus rudis as material. In fact with long slender poles of 
Eucalyptus tereticornis at Edison, such a remarkably rapid backward 
flow of eosin was observed (105 em. in one minute) in the afternoon 
as to compel the conclusion that after all, the force responsible for 
this movement under such conditions must be negative pressure pro- 


PLATE 12 
Fig. 1. Showing extent to which the leaves can draw on the water in the fruit. 
Both shoots were cut at the same time and had approximately the same leaf 
area. All cuts were sealed with vaseline. The fresh-appearing leaves on the 
shoot at the left have maintained themselves at the expense of water in the 
fruit. Note the difference in reflection of light from the two fruits. See 
Experiment 1. 


Fig. 2. Photograph illustrating an orange shoot so arranged as to be able to 
draw water from one end and eosin solution through the pared apex of a small 
fruit at the other. In spite of this double supply a large water deficit occurred, 
and eosin was drawn back from the container on the right to the leaf next to the 
water container on the left. See Experiment 6. 


[54] 


UNIV. CALIF. PUBL. AGR. SCI. VOL. 3 [HODGSON] PLATE 12 


o ais) 


fy dy 
Dee's | 


“UNIVERSITY OF CALIFORNIA PUBLICATIONS—(Continued) 


BOTANY. —W. A. Setchell, Editor, Price per volume, $3.50. Volumes I (pp. 418), If (pp. 
360), III (pp. 400), and IV (pp. 397) completed. Volumes V, VI, and VII 
in progress. 


Vol. 8. 1. Compositae of Southern California, by Harvey Monroe Hall. Pp. 1- 
802; plates 1-3, with a map. December, 1907 -... cc nent eneeseeens $.00 

2. The Origin, Structure, and Function of the:Polar Caps in Smilacina 

amplezicaulis Nutt., by H. D, Densmore. Pp. 803-330; plates 4-8. 
December, 19S ees acannon chen cen gcse cen anne nn tebawene 35 

$, 4. (In one cover.) . The Value of Sodium to Plants by Reason.of Its 

Protective Action. On the Effects of Certain Poisonous Gases on 
Plants.. By W.J. V. Osterhout.. Pp. 331-340. June, 1908 - omnes oars (1 

5. Contributions to the Knowledge of the California Species of “Crusta- 

ceous Corallines, I, by Maurice Barstow Nichols. Pp. 341-348; 
Plate 9. December, 1908 oa... ----.c0e--n-e-ceeeeneceettneeseensneerentatnetneneeenenemnnes 10 

6. Contributions to the Knowledge of the California Species of Crusta- 

ceous Corallines. II; by Maurice Barstow Nichols. Pp. 349-370; 
Plates 16-13. April, 1909.12. .cen.-----,--nencnoen nce sene nent esters en eennen es ensseanstnens ane 15 

7. New Chlorophyceae from California, by Nathaniel Lyon Gardner, Pp. 
$71-375; plete 14. April, 1909 

8. Plantae Mexicanae Purpusianas, by T. 8. Brandegee. Pp. 377-396. 
ray, 1909 anna cece caetceetececpeanntcnnecenenenscenateccensernanecenenentoceresenen Sea | 

Index, pp. 397-400. 


Vol. 4. 1, Studies in Ornamental Trees and Shrubs, by Harvey Monroe Hall. Pp. 


1-74; plates 1-11; 15 text-figures. March, 1920 22... sen ecnsyenstensnae 75 

2. Gracilariophila, a New Parasite on Gracilaria confervoides, by Harriet 
L. Wilson. Pp. 75-84; plates 12-13. May, 1910 2. ..2.2.---s-eereneeeee 10 

$3. Plantae Mexicanae Purpusianae, U, by T. 8. Brandegee,. Pp. 85-95, 
gE ais 15) 1 pe mt sal RE ae scape estne eran oo ee eee eo 10 

4. Lewvenia; a Now Genus of Flagellates, by N. L. Gardner. Pp. 97-106; 
plate 14. “Miay, 1910 sxe icc E eachensedantsrcpe en cece ra cennnamnensnnetreste +10 

5. The Genus Sphaerosoma, by William Albert Setchell. Pp. 107-120): 
plate 15. May, 1910 enn eee n catch cec tence sere qeceysandesensebeenanresecees 15 

6. Variations in Nuclear Extrusion Among the Fucaceae, by Nathaniel 
Lyon Gardner. Pp. 121-136; plates 16-17. August, 1910 . Lee AG 


7. The Nature of the Carpostomes in the Cystocarp of Ahnfeldtia Gigarti- 
noides; by Ada Sara McFadden, Pp. 137-142; plate 18. February, 


SOG a cece Sa ep ia a are nbc arpa matcoanen Somasnpaees 08 
8, On a Colucodasya from Southern California, by Mabel Effie McFadden. 
Pp. 148-150; plate 19. February, 1911 «.....-2 02 -scenttceeeeeee 305 
9. Fructification of Macrocystis, by Edna Juanita Hofiman. Pp. 151-158; 
pbs aot Ree! i cht a oa ae AD 8 Deion Gee onan eae oy a NDR ne ae ag Se  - 05 
10. ‘Erythrophyllum delesserioides J. Ag., by Wilfred Charles Twiss. Pp. 
159-176; plates 21-24. March, 1910 2-.o...-i.-sneeo ewes ccnp tieeen nee nonce 15 
11. Plantae Mexicanae Purpusianae, IH, by T. S. Brandegee, Pp. 177-194. 
‘ 3 ; ALE ssp Be Bt a RS Se NS are aR ats oe AR SA ERAS ce heres earl set 15 
Se cote 12. New and Noteworthy California Plants, I, by Harvey Monroe Hall. 
; Papo TGb-20S so. VTA e Yh LOT a aoe lah aapmerpactbe encead laren 15 
18. Die Hydrophyllaceen der Sierra Nevada, by August Brand. Pp. 209- 
A Pie ER, PoP 8 he ES Sap aD ae eS te eS OD RRS na 20 
be 14. Algae Novae et. Minus Cognitae, I, by William Albert Setchell. Pp. 
BDO-OGRe: pilatesc25-Sh. 4 WAY, LOUD 8. Sele ca ancenap stn cuba cena nodectatasicent 40 
15. Plantae Mexicanae Purpusianae, IV, by Townshend Stith Brandegee. 
Py. 269-269 tina 2 391 a ee et cece 15 


-16. Comparative Development of the Cystocarps of Antithamnion and 
Prionitis, by Lyman L. Daines. Pp, 283-302; plates $2-34.. March, 


40122 tac pees. 

7. Fungus Galls of Cystoseira and Halidrys, py. Lulu M. Estee. Pp. "305- 316; 
Hiate: Sia March 1 OLS oo eo oe ee a cae osamnmanens 10 

18. New Fucaceae, by Nathaniel L. Gardner. Pp. 317-374; plates 36-53. 
Fe 5 ES ys EE i SE ES ea NO ee ae hte Baa ane eae aN See Rahs eee 75 

19. Plantae Mexicanae Purpusianae, V, by Townshend Stith Brandegee. 
a Fos 1 RO Rs Pots bs Es ea ei eS aoe Ser aera ice ee Se pT one _. 15 


- Index, pp. 889-397. 

Vol. 6. 1. Studies in Nicotiana I, by William A. Setchell. Pp. 1-86; plates 1-28, 
BIGCOMI GO 1 OL as, sca en Ss he cer en ec ge cepa ah Pa earned cacoeenbecde 1.25 

-2. Quantitative Studies of Inheritance in Nicotiana Hybrids, by Thomas 
-H. Goodspeed. Pp. 87-168; plates 29-34. December, 1912 .._........... 1.00 

8, Quantitative Studies of Inheritance in Nicotiana Hybrids Il, by Thomas 
H. Goodspeed. Pp, 169-188. January, 1913 2202... ee 20 

4. On the Partial Sterility of Nicotiana Hybrids made with N. Sylvestris 
as a Parent, by Thomas H. Goodspeed. Pp, 189-198. March, 1913... _.10 


LIBRARY OF ¢ 


suv 


UNIVERSITY OF CALIFORNIA oo 
B. Notes on the Germination of Tobacco Seed, by Thomas Harper Good- 


Tas (5 OES i « Tita st a1” Fa Zoe BS I Re ce eee a RRR cope 25 
6. Quatititative Studies of Inheritance in Nicotiana Hybrids, ITI, by. sae 
Thomas Harper Goodspeed. Pp. 223-231. April, 1915 ..0..2...0/.... 10 


7. Notes on the Germination of Tobacco Seed, II, by Thomas Harper Good- 


speed... Pp. 238-248, Tune; 1615 <i SN ee ee 15 


8. Parthenogenesis, Parthenocarpy, and Phenospermy in Nicotiana, by : 
; Thomas Harper Goodspeed. Pp. 249-272, plate 35. July, 1915 2... 25 
9. On the Partial Sterility of Nicotiana Hybrids made with N. sylvestris 
as @ Parent, II, by T. H. Goodspeed and A. H. Ayres. Pp. 273-292, { 
pl. 36. October, B32 Ns ead led prc ete ete CNN oe eth = Seems 2H I Pos wed ~ 20 
10. On the Partial Sterility of Nicotiana Hybrids made with W.. sylvestris 
as a Parent, IIT: An Account of the Mode of Floral Abscission in the... 
F, Species Hybrids, by T. H. Goodspeed and J. N. Kendall. Pp. 293- 
2995 NOV Pier 1916/22 ee ob as espe ccencan .05 
11. The Nature of the F, Species Hybrids between Nicotiana sylvestris and z 
Varieties of Nicotiana Tabacum, with: Special Reference to the Con- 
ception of Reaction System Contrasts in Heredity, by T. H. Good- 


speed and R. E. Clausen. Pp. 301-346, pls. 87-48. January, 1917 .... 45 


Vol. 6 1. Parasitic Florideaze, I, by William Albert Setchell. Pp. 1-34, plates 1-6... 
795 th gb Paget 03 Spe eM nN Gt cei tee SR cea ARS UNSER Ee ACER IN a a RRS ENE | cs 3865 
2. Phytomorula regularis; a Symmetrical Protophyte related to Coelastrum, ae 


by Charles Atwood Kofoid Pp. 35-40, plate 7 April, 1914 8. 05 


8. Variation in Oenothera ovata, by Katherine Layne Brandegee. Pp. 41- ~ 
BO; Plates 8-9, Jima LOVE ae aes ee hss en cee eared eeaneetatee 10 
4, Plantae Mexicanae Purpusianae, VI, by Townshend Stith Brandegee. 


PpDleTh = AMR Ust LORE Sos es cre oo oe a a dee 25 


5. The Scinaia Assemblage, by William A. Setchell. Pp..79-152, plates 10-- 

ABs* OCtower;. BOL pea ee eee ip ran ap Re che cae odpnges anata ee eee em on operepere By is 
6. Notes on Pacific Coast Algae, I; Pylaielia Postelsiae, n. sp., a New Type 

in the Genus Pylaiella, by Carl Skottsberg. Pp. 153-164, plates 17-19. 3 

BEF ggg E28 A Spend mia elon St paren mma b Da omaas elereat on AEN rey a. Ueateopr re einer te es 10 
7. New and Noteworthy Califoraian Plants, II, by Harvey Monroe Hall. 


Pp. 165-176, plate 20.° October, 1945 cc... .clsctcccstscstsateccaccensnssalecdecscesnes 1240; 


8. Plantae Mexicanae Purpusianae, VIL, by IT. S. Brandegee, Pp. 177-197. 


October, 101565 eee Oe ea a Ren a 


9. Floral Relations among the Galapagos Islands, by A: L. Kroeber. Pp. 
199-0205" “March; “4916.2 223 ss Stet FS a as ee 20 
10. The Comparative Histology of Certain Californian Boletaceae, by ; 


Harry 8S. Yates. Pp, 221-274, plates 21-25. February, :1916 ..--.252. 50 


11. A revision of the Tuberales of California, by Helen Margaret Gilkey, 


Pp. 275-356, plates 26-30. © March, 1916 oi... ...cecce cc ercetensngetennemt cncnnenesnne 80 
12. Species Novae vel Minus Cognitae, by T. 8. Brandegee. ER. 357-361, 2 
Nc wo 4 Pan 28 1 Rape neat a eagle oi ULE Pere Ree rier po uAe ey eR No ieeom So OD. 


VoL 7. Notes on the Californian Species of Trillium. 
1. A Report of the General Results of Field and Garden Studies, 1911- 
1916, by Thomas Harper Goodspeed and Robert Percy Brandt. Pp. 


1-24;"pls; I-47 October; 195. Ge ee east sary acto nme tne eoeeab eae 25 


2. The Nature and Occurrence of Undeveloped Flowers, by Thomas Harper 
Goodspeed and Robert Percy Brandt. Pp. 25-38, pls. 5-6. October, : 
UE ee ssi oe Bie ati ecto Se paneer endaetaek ox ou IBRuRaN Gece Eis Se and aaa 16 

8. Seasonal Changes in Trilliwm Species with Special Reference to the 
Reproductive Tissues, by Robert Percy Brandt. Pp. 39-68, pls. 7-10. 


Dacember, 1916.22. ik he ae aA ae cet ease haber asned beret es 30 


4, Teratological Variations of Trillium sessile var. giganteum, ne ‘Thomas 
Harper Goodspeed. Pp. 69-100, pls. 11-17. January, 1917 .. OES ne (i 


AMERICAN ARCHAEOLOGY AND EZTHNOLOGY,—A. L.. Kroeber, Editor. Price per. 
volume, $3.50 (Voiume I, $4.25). Volumes I-X completed. ‘Volumes XI and xIt ys Sak 


progress. 5 re 
GEOLOGY.—Bulletin of the Department of Geology. Andrew ©. Lawson and John aK 
Merriam, Editors, Price per volume, $3.50. Volumes I (pp. 428), IZ (pp. 450), IIT 
(pp. 475), IV (pp. 462), V (pp. 458), VI-(pp. 454), VIL (pp. 504), VIIL (pp, BES), anal 
IX (pp. 545) completed. Volume X in progress. 


Other series in Classical Philology, Economics, Education, Egyptian Archaeology, ‘Engi. : ‘ 
neering, Entomology, Geography, Graeco-Roman Archaeology, History, Mathematics, Modera f 


Philology, Pathology, Philosophy, Psychology, Physiology, Semitic Philology. 
UNIVERSITY OF CALIFORNIA’ CHRONICLE.—An. official record. of University life, 


issued quarterly, edited by a committee of the faculty. Price $1.00 per year. Current 


volume No. XVIX. 


ADMINISTRATIVE BULLETINS OF THE UNIVERSITY OF CALIFORNIA, —Eaitea Be! ears 


the Recorder of the Faculties. Includes the Register, the President's cae 
Secretary’s Report, and other official announcements. 


x 


Bg SE pas